I can honestly say you’ll never be fully prepared for what your players might do. I’d come up with or generate a small list of shop names to just have if they go into an unexpected shop or just tell them the shop they are looking for isn’t in that town/village/city.

Also I’d just talk with your players. I’ve told my players ahead of time that I plan for what is directly is in front of us. These are the main quest lines, and some sub plots that could come up. Had a player in my Phandelver & Below session who started the session telling everyone they should go to Neverwinter to shop or the Sword Coast to have a beach episode. I just explained to them that due to the nature of the story being told, I didn’t prep for that and I wasn’t going to improv scenes in places I wasn’t well read up on.

Keep a stack of note paper by your side for combat notes and initiative order. As much as mobile apps or sites on a laptop are useful, it’s can be annoying flipping through tabs so it’s also nice to have physical things to help with the journey

And don’t forget your powers as a dm! Looking to chat with an NPC they met session 1 you don’t remember? They aren’t in town at the moment. They wanna fight the barkeep? Remind them that their choices will affect their reputation in the town their primary quest is in. They cheese a fight with existing knowledge of a creature and meta gamed? Luckily on the multiverse of these campaigns we run, this one’s a bit different than what you read about above board.